This invention relates in general to thermometers intended to measure the core temperature of a living being and, more specifically, to measure that temperature by measuring and analyzing infrared radiation from the tympanic membrane.
The measurement of the core temperature of a body has been long used in medical diagnosis and treatment. The most common method has been to measure temperature with a tubular glass thermometer containing mercury by insertion in the mouth or rectum, placing under the arm, etc. Breakage of those thermometers in use is a constant danger. Seriously ill or injured patients may bite through the thermometer or make abrupt movements which cause breakage during the 2-3 minutes required to obtain an accurate maximum temperature. Further, mouth or rectum temperatures may not always be representative of true body core temperature and do not change as rapidly as core temperature. These thermometers require sterilization when used with a number of patients to prevent cross-contamination and must be shaken down to reduce the displayed temperature since they only measure increasing temperature. These steps take significant time in a busy medical office or hospital and may be overlooked with serious consequences.
Considerable effort has been expended in recent years towards improved body temperature measuring devices using electronic probes of one sort or another. Often, the glass thermometer is simply replaced with a metal or plastic housed temperature sensing probe inserted in the mouth or rectum. While somewhat safer than the glass thermometers, these continue to be slow in measuring temperature and do not precisely indicate accurate, up to the minute, body core temperature.
Recently, it has been determined that the tympanic membrane within the ear canal is an excellent site for determination of the core temperature of a body due to its proximity to the external carotid artery which supplies blood to the hypothalamus. The hypothalamus has been shown to be the site of the body's core temperature. Patients show changes in core temperature at the tympanic membrane prior to peripheral sites such as the mouth or rectum. This allows the attending physician to more quickly respond to possible complications.
Prior ear thermometers suffer from a number of problems. They are difficult to calibrate to provide accurate temperatures in varying ambient temperature conditions and have repeatability problems. The previous ear thermometers used rigid metal tube "waveguides" using a metal coating such as gold to increase the reflectivity of the inner surface. Since these work according to principles of classic optics with the infrared radiation bouncing off the walls from one end to the other there are severe losses with a tube of the necessary length. For example, assuming a reflectivity of 97%, 20 "bounces" will reduce the signal by about 50%. The tube must be straight and must have a large diameter to reduce the number of bounces. Typical of such ear thermometers is that described by Fraden in U.S. Pat. No. 4,797,840.
Another prior ear thermometer is described by O'Hara et al in U.S. Pat. No. 4,790,324. This thermometer uses a probe including waveguide tube to direct infrared radiation to a thermopile which is kept at a constant temperature by a heater. In order to calibrate the unit, before use the probe is connected to a chopper unit which is kept at a constant temperature by a second heater system to establish a reference temperature. Then the probe is removed from the chopper, a disposable speculum is placed over the probe which is then inserted in the patient's ear and a temperature reading is taken. This complex calibration method is prone to errors, requires several heaters and may give erroneous readings if the calibration targets are not at the precise intended temperatures or there is a delay between calibration and ear temperature measurement.
Thus, there is a continuing need for improved ear thermometers of improved simplicity, accuracy and usefulness.